There have been a technology for simultaneously acquiring outputs with respect to a plurality of reference signal sequences as disclosed in JP-A 2003-1708048 and a technology for processing a plurality of oncoming signals received by an array sensor device comprising a plurality of sensors as disclosed in JP-A 9-219616.
FIG. 32 is a diagram showing an arrangement of a wireless communication system of the above type. Receiving apparatus 800 employs a plurality of reception antennas 800-1 through 800-4, and demodulates received signals according to a demodulating process based on maximum likelihood sequence estimation.
In FIG. 32, it is assumed that signals sent from three transmission antennas (not shown) are received by receiving apparatus 800 having four reception antennas 800-1 through 800-4, and each transmission antenna is sending either one of 16-valued signals c1 through c16.
Receiving apparatus 800 has four reception antennas 800-1 through 800-4 each for receiving a signal. Channel coefficient estimator 802 is supplied with the received signals as its inputs, estimates channel coefficients between the transmission and reception antennas, and outputs a channel matrix. Maximum likelihood sequence estimator 803 is supplied with the received signals and the channel matrix as its inputs and estimates transmitted sequences.
In the above example, if either one of 16-valued signals c1 through c16 is sent from the three transmission antennas, then maximum likelihood sequence estimator 803 comprises 4096 error calculators 804-1 through 804-4096 and one signal selector 805.
Each of error calculators 804-1 through 804-4096 is in the form of error calculator 804 shown in FIG. 33. In first-stage error calculator 804-1, transmitted symbol generator 811 generates and outputs transmitted symbols s1-1, s1-2, s1-3 with respect to each of the antennas.
Received signal replica generator 812 is supplied with the transmitted symbols and the channel coefficients as its inputs and generates and outputs received signal replicas.
Error calculator 813 is supplied with the received signals and the received signal replicas as its inputs and calculates an error signal. The transmitted symbols generated by transmitted symbol generator 811 are for either one of signals c1 through c16, and error calculators 804-1 through 804-4096 generate mutually different transmitted symbols.
Received signal replica generator 812 generate four received signal replicas r1-1, r1-2, r1-3, r1-4 represented by:r1-1=h11s1-1+h12s1-2+h13s1-3 r1-2=h21s1-1+h22s1-2+h23s1-3 r1-3=h31s1-1+h32s1-2+h33s1-3 r1-4=h41s1-1+h42s1-2+h43s1-3 where h11, h12, h13, h21, h22, h23, h31, h32, h33, h41, h42, h43 represent the channel coefficients between the transmission antennas and reception antennas.
Error calculator 813 is supplied with the received signals and the received signal replicas as its inputs and calculates error signal e1 according to the equation:e1=|r1−r1-1|2+|r2−r1-2|2+|r3−r1-3|2+|r4−r1-4|2 
First-stage error calculator 804-1 outputs generated transmitted symbols s1-1, s1-2, s1-3 and calculated error signal e1. Similarly, second-stage error calculator 804-2 outputs transmitted symbols s2-1, s2-2, s2-3 and error signal e2. 4096th-stage error calculator 804-4906 outputs transmitted symbols s4096-1, s4096-2, s4096-3 and error signal e4096.
Signal selector 805 is supplied with the transmitted symbols and the error signals output from 4096 error calculators 804-1 through 804-4096, as its inputs, selects a minimum error, and outputs transmitted symbols which give the minimum error. In this manner, the transmitted signals are modulated.